The invention relates to a clamping-roller freewheel for an adjustment device in a motor vehicle, in particular in a motor vehicle seat, the clamping-roller freewheel comprising a) a housing having a cylindrical inner surface defining an axis, b) at least one pair of rollers having two rollers, the rollers being in contact with the inner surface, c) an output shaft central to the axis, and d) a clamping member which is located on the side of the rollers opposite to the inner surface and rotationally connected to the output shaft. The clamping-roller freewheel is also named clamping-roller freewheel hub or clamping-roller device.
Such a clamping-roller freewheel is known from DE 10 2009 028 213 A1. Such clamping-roller freewheels are preferably used for step-by-step ratchet mechanisms as they are known, for example, from EP 1 152 168 B1 and DE 195 40 631 C2.
With regard to further prior art, reference is made to EP 497 007 B1, in which, however, inclined clamping surfaces are disposed on the housing and not on the clamping member. The clamping member has a cylindrical outer surface.
In the case of such clamping-roller freewheel, a locking moment that is as large as possible is desired; it is supposed to be greater than 60 Nm, with Hertz pressure being taken into account. The minimum ultimate moment is supposed to be greater than 200 Nm. It is another goal that, over the angle of rotation, the locking moment at first has a smaller gradient and then, above a certain angle of rotation, a larger gradient. Above a further angle of rotation, the clamping action is supposed to be maintained at as high and constant a level as possible, before permanent deformation or damage sets in.
The known clamping-roller freewheel comprises n rollers. Half of them are responsible for one direction of rotation, the other half for the other direction of rotation. Therefore, the locking moment in one direction is only effected by half, n/2, of the rollers. The other half of the rollers is passive in this case. In order to increase the locking moment, the number n of the rollers in the clamping-roller freewheel could be increased. However, an increase in the size of the clamping-roller freewheel is not desired. The space in the clamping-roller freewheel is limited.